This invention relates to particle acceleration apparatus, and in particular to a device for the acceleration of helium ions by a tandem-type direct-voltage accelerator. In tandem accelerators, negative ions are produced and accelerated by a direct voltage to a terminal which is maintained at a high positive voltage. Within this high-voltage terminal the negative ions are caused to pass through a stripping device (either a gas or a foil) so that a substantial number of them are converted to positive ions, which are then accelerated away from the positive terminal back to ground potential, where they may be used for various purposes. In this way the ultimate energy of the particles is at least twice that which would correspond to acceleration by a direct voltage of the amount on the high-voltage terminal; the production of multiply-charged particles results in even higher energies.
A common application of tandem accelerators has been the use of this principle in direct-voltage accelerators designed for the maximum voltage attainable by the state of the art, in order to achieve particle energies higher than those attainable by "single-pass" acceleration. However, the tandem principle has also found use in lower-voltage accelerators, since it permits the manufacture of smaller "multi-pass" accelerators to achieve the same end result as that achieved by larger "single-pass" accelerators.
Because of the relatively high initial cost and high maintenance requirements of particle accelerators, they have often been designed for versatility. Thus, most tandem accelerators have been designed for the acceleration of virtually all types of ions for various purposes. This has meant that these accelerators were required to be capable of variation in their parameters, such as the electric and magnetic fields which cause deflection and focusing of the ion beam.